1. Field of the Invention
The present invention relates to a thermal transfer sheet adaptable to a thermal transfer printer using a heating mean such as a thermal head and a laser and, particularly, to a thermal transfer sheet capable of easily producing a printed product with metallic luster.
2. Description of the Related Art
A melting type thermal transfer system has been known, in which a thermal transfer sheet is composed of a substrate sheet and a coloring layer which is obtained by dispersing a coloring agent such as a pigment or a dye in a heat-meltable binder such as wax or a resin and supported by the substrate sheet such as a plastic film, and energy corresponding to image information is applied to the thermal transfer sheet by means of a heating device such as a thermal head, and thus the coloring agent is transferred from the thermal transfer sheet to an image-receiving sheet such as paper or a plastic sheet together with the binder.
An image printed by this melting type thermal transfer system has high density and superior sharpness and is therefore suitable for the recording of binary images such as characters and line drawings. In addition, when plural coloring layers such as yellow, magenta, cyan and black are used for printing and recorded on the image-receiving sheet in a superposed manner with the use of one or more thermal transfer sheets, a multicolor or full color image can be formed by subtractive color mixing.
There is an increasing demand for a melting type thermal transfer system applicable to production of a printed product having metallic luster or metallic brightness and thus excellent in design, appearance or decoration.
In order to meet such a demand, Japanese Patent Laid-open Publication Nos. Hei 10(1998)-16415 discloses a thermal transfer sheet having metallic luster, in which an anchor layer for vapor deposition, a metallic vapor deposition layer and an adhesive layer are composed on one side of a substrate in this order from a side near the substrate.
Japanese Patent Laid-open Publication Nos. sho 63(1988)-290789 discloses a thermo-sensitive transfer material in which an ink layer composed by dispersing a metallic powder pigment such as aluminum and bronze in a heat meltable vehicle is disposed on a support film.
However, in a case where the metallic vapor deposition layer is formed on the substrate so as to be peelable, special methods such as a gaseous phase process including vacuum deposition and sputtering are required to form the metallic vapor deposition layer. In such a method, the metallic vapor deposition layer is formed into a thin film with a thickness of about 200-600 xc3x85 on the substrate, and it poses some problems that the metallic vapor deposition layer is liable to be cracked by impact or exposing outdoors because of its poor flexibility, and that the metallic vapor deposition layer is a thin film liable to transmit the light and thus being inferior in hiding property for hiding the ground face, and further that a process cost is very expensive.
On the other hand, in a case where the ink layer dispersing the pigment of metallic powder in the heat meltable vehicle is formed on the support film, the printed product is inferior in the metallic luster and the hiding property than the above described type using the metallic vapor deposition layer and therefore unsatisfying in qualities.
Accordingly, it is an object of the present invention to provide a thermal transfer sheet having a high metallic luster and hiding property and a good reproduction of color even if a colored receiving paper is subjected to printing, and thus capable of forming a printed product excellent in qualities including design, appearance or decoration, and further capable of being manufactured at a low cost by an easy process.
To achieve the above mentioned object, the present invention provides a thermal transfer sheet which comprises a substrate film and a metallic layer disposed on one side of the substrate film, the metallic layer being comprising leaf-shaped aluminum powder.
The leaf-shaped aluminum powder to be preferably used is one obtainable via a process in which an aluminum film is formed by a vapor deposition on a peelability facilitating surface of a carrier sheet, and the aluminum film is peeled off the carrier sheet and finely divided.
It is preferable that the thermal transfer sheet of the present invention is further provided with a peelable layer which is disposed between the substrate film and the metallic layer. The peelable layer facilitates the metallic layer to peel off the substrate film at the time of thermal transfer printing.
It is preferable that the peelable layer contains a coloring agent. The peelable layer containing the coloring agent can reproduce a hue of a chromatic color having metallic luster such as golden, copper and bronze colors.
It is preferable that the thermal transfer sheet is further provided with an adhesive layer as an outermost layer which is disposed on the metallic layer, and the adhesive layer can firmly bond the metallic layer to a surface of a transfer receiving material.
The thermal transfer sheet of the present invention has a structure in which the metallic layer containing at least leaf-shaped aluminum powder is disposed on one side of the substrate film. When the thermal transfer sheet of such a structure is used to form an aluminum coating film on a printed surface, the aluminum coating film thus formed has a scaly configuration composed of aluminum fine peaces, in which many peaces of the leaf-shaped aluminum powder come to the surface of the aluminum coating film and almost closely arranged along a lateral direction with edges of the respective peaces of the leaf-shaped aluminum powder being in contact or overlapped with each other, thus producing a highly smooth coating of aluminum and obtaining a printed product which has a high hiding property and metallic luster and is excellent in qualities including design, appearance or decoration.
Furthermore, the metallic layer comprising the leaf-shaped aluminum powder can be easily formed on the substrate film by a coating process and does not depend on the gaseous phase process such as a vapor deposition, and therefore it is not expensive to produce the thermal transfer sheet of the present invention.